In recent years, attention is being given to a projection display apparatus using various light modulation devices as a large-screen projection video apparatus. In the case of performing a large-screen display, brightness of a displayed image can be named as the most important item.
Thus, attention is being given to a multi-lamp illumination system using multiple lamps and capable of improving optical output as the projection display apparatus. As for the brightness, it is important to illuminate the light modulation device as an image display device with as little loss of luminous fluxes radiated from the lamps as possible, that is, as efficiently as possible. For that reason, it is desirable to improve efficiency of the light source apparatus of collecting lamp radiation light.
FIG. 11 shows a conventional multi-lamp optical system having two light source apparatuses configured by the lamp and concave mirror provided therein. The light radiated from a light source apparatus 1 gets incident on a hollow rod integrator 2 made of glass poles or mirrors glued together. It repeats total reflection inside the glass in the case of the glass poles, or repeats reflection in the case of the type having the mirrors glued together. It is possible, by means of the reflection inside the rod integrator 2, to create the luminous fluxes of homogeneous in-plane brightness on an emission opening plane of the rod integrator 2. Furthermore, it is possible, with a relay lens 3 after this, to focus the luminous fluxes of high in-plane homogeneousness on a light modulation device 4 of performing an image display so as to display the image provided on a screen by a projection lens as the image of which in-screen brightness is highly homogeneous.
Next, as for improvement in the efficiency of the conventional light source apparatus of collecting lamp radiation light, a basic configuration of the light source apparatus as a first conventional example is shown in FIG. 12 (refer to Japanese Patent No. 2543260 and Japanese Patent No. 3151734 for instance). In the case of this light source apparatus, the light radiated from light-transmitting planes 5a and 5b of a light-emitting portion 5 of the lamp is collected on a focus X by a first concave mirror 6 having an ellipsoidal or paraboloidal reflection plane form. The radiation light from the light-transmitting planes 5a and 5b of the light-emitting portion 5 of the lamp not collected by the first concave mirror 6 is reflected on a second concave mirror 7 consisting of a spherical mirror for instance and having its reflection plane facing the reflection plane of the first concave mirror 6, and is then returned to the vicinity of the light-emitting portion 5 of the lamp so as to be collected on the focus X by the first concave mirror 6.
Thus, the first concave mirror 6 and the second concave mirror 7 are used in a state of having their reflection planes facing each other, the second concave mirror 7 having the outermost diameter larger than the outermost diameter in a vertical direction to an optical axis of the first concave mirror 6, that is, a straight line connecting a luminescence center 5c of the light-emitting portion 5 to the focus X. The light radiated from the light-emitting portion 5 of the lamp is thereby taken in as much as possible so as to be collected by the first concave mirror 6.
The basic configuration of the light source apparatus as a second conventional example is shown in FIG. 15 (refer to Japanese Patent No. 2730782 and Japanese Patent No. 3350003 for instance). In the case of this light source apparatus, a light source 10 of the lamp is placed on a focus Y of an ellipsoidal mirror or paraboloidal reflecting mirror as a first concave mirror 8. The first concave mirror 8 is provided at an angle capable of reflecting all the radiation light from a light-transmitting plane 10a of the light source 10. This light source apparatus coincides with the first conventional example in that the light radiated from the light-transmitting planes 10a of the light source 10 and reflected on the spherical mirror as a second concave mirror 9 is returned to the vicinity of the focus of the first concave mirror 8 and as much light radiated from a light-transmitting portion 10 as possible is thus taken in together with the light radiated from the light-transmitting plane 10b and directly collected by the first concave mirror 8.
However, they are different in that the first conventional example has the opening of the second concave mirror 7 in a vertical plane against an optical axis direction of the first concave mirror 6 whereas the second conventional example has the second concave mirror 9 placed in a horizontal direction against the direction of the optical axis of the first concave mirror 8, that is, the straight line connecting a luminescence center 10c of the light-emitting portion 10 of the lamp to the focus Y.
As shown in FIG. 11, the conventional multi-lamp optical system has the configuration in which the light radiated from multiple light source apparatuses gets incident on the rod integrator 2 which is homogeneous lighting means. However, a transmissive/reflective liquid crystal of displaying the image and the light modulation device called a DMD (Digital Micro-mirror Device) have a luminous flux incident angle range capable of substantially modulating the light and an image display effective area capable of displaying the image. For this reason, due to the relation of Helmholtz-Lagrange which is a basic formula of imaging optics, an output angle range of the light according to the size of an outgoing side opening 2b of the rod integrator 2 in an imaging relation with the relay lens 3 is uniquely decided by the relay lens 3.
In this case, if the outgoing side opening and the incident side opening of the rod integrator 2 are of an equal size, the output angle range is equal to the incident angle range. If the outgoing side opening and the incident side opening are of different sizes, the incident angle range is in accordance with the size of the incident side opening induced by the relation of Helmholtz-Lagrange, and so only the luminous flux within this angle range is projected onto the screen via the rod integrator 2, relay lens 3, light modulation device 4 and projection lens.
For this reason, in the case of the light source apparatus having a single concave mirror 1 capable of collecting more lamp radiation light, the incident angle range of the rod integrator 2 is limited. Therefore, there is a problem that a distance between the concave mirror 1 and an incident side opening 2a of the rod integrator 2 becomes long and an optical spot size formed by the concave mirror 1 becomes large so that an amount of light to be taken in by the opening of the rod integrator 2 decreases.
As with the light source apparatus of the conventional multi-lamp optical system shown in FIG. 11, the light source apparatus of the first conventional example shown in FIG. 12 is in a form of rotation symmetry to the optical axis of the first concave mirror, that is, the straight line connecting the luminescence center 5c of the light-emitting portion 5 of the lamp to the focus X. It has a problem that, in the case of forming a similar multi-lamp optical system, the amount of light to be taken in by the opening of the rod integrator 2 decreases. It also has a problem that its outer shape becomes large.
The light source apparatus of the second conventional example shown in FIG. 15 is in a form of non-rotation asymmetry to the optical axis of the first concave mirror, that is, the straight line connecting the luminescence center 10c of the light-emitting portion 10 of the lamp to the focus Y. Its outer shape can be smaller than that of the first conventional example. The luminous fluxes formed by collection of light can also be of non-rotation symmetry, and it is possible, even in the multi-lamp optical system of FIG. 11, to reduce the distance between the first concave mirror 8 corresponding to the first concave mirror 6 and the incident side opening 2a of the rod integrator 2.
However, the light source apparatus of the second conventional example shown in FIG. 15 has the following problem. The reflection plane having the second concave mirror 9 formed thereon reflects all the light radiated from the light-transmitting plane 10a as shown in FIG. 15. Nevertheless, all the reflected light is not collected by the first concave mirror 8, but a part of it is radiated outside so as to become an impediment to light collection efficiency.
To collect all the reflected light of the second concave mirror 9 on the focus Y, it is necessary to expand the reflection plane of the first concave mirror 8 by an equivalent of an area 150. However, this leads to a larger size of the light source apparatus so that the light collection efficiency and the larger size of the light source apparatus will be in a trade-off relation.
The light radiated from a lamp 5 and directly reaching the first concave mirror 6 in an upper half in the light source apparatus of the first conventional example of FIG. 12 is taken in by the second concave mirror 9 in the light source apparatus of the second conventional example of FIG. 15. In this case, the light reflected on the second concave mirror 9 passes through the vicinity of the light-emitting portion 10 of the lamp again so as to get to the first concave mirror 8. In the case of using a metal halide lamp or a mercury lamp as the lamp, much of the light passing through the light-emitting portion again is lost due to light absorption and light scattering of light-emitting materials and materials configuring the lamp. Thus, it has a problem that the amount of luminous fluxes emitted to the focus Y is consequently reduced and optical usable efficiency is lowered as the entire light source apparatus.
The present invention was made in order to solve these problems of the conventional examples, and an object thereof is to provide the light source apparatus of which optical usable efficiency is not lowered by miniaturizing it and the lighting apparatus and projection display apparatus of higher efficiency and capable of miniaturization by having the light source apparatus.